Multiple Zero Crossings Research Articles

Compensation of Discontinuous Conduction in Three Phase Voltage Source PWM Inverters

Nowadays the increasing utilization of alternative energy sources demand power converters capable of delivering high quality energy to the low voltage grid. Good dead time compensation and linear operation are essential to keep low order harmonics at acceptable levels. High-current operating conditions are well handled by traditional methods, but low current behaviour and waveforms with multiple zero crossings within a switching period are problematic, especially at low load conditions at or below 10% load. Such conditions often occur in the battery chargers of electric cars. Power quality is also essential for sensorless drives, as the accuracy of the output voltage is very important especially at low rotational speeds. This paper describes the identified cases of discontinuous conduction during dead time. Based on the voltage and current waveforms of the three phase inverter, an improved dead time compensation method is shown for symmetric PWM controlled inverters. The compensator uses already available measurement data, and compensates the resulting error voltage at duty cycle level. The described method can be used for any type of three phase modulation. A similar approach can also be used for two phase modulations.

Special‐angle‐based signal injection sensorless control of IPMSM for suppressing multiple zero‐crossings of phase current

Pulsating high-frequency signal injection has the problem of multiple zero-crossings when the phase current crosses zero-point, which deteriorates the distortion of high-frequency current caused by the zero-current-clamping effect. Thus, the accuracy of position observation is affected. To suppress multiple zero-crossings, improved sinusoidal and square-wave signal injection schemes are proposed. First, the relationship between the injection angle of the high-frequency signal and the phase of the high-frequency response current amplitude function is analysed. Based on the relationship, a special injection angle is calculated. By injecting the pulsating signal in the obtained special angle, the phase of the high-frequency current is shifted. The amplitude of the high-frequency response current is minimum when the fundamental frequency current crosses zero, thus reducing zero-crossing points of phase current. Furthermore, the error signal extraction scheme applicable to arbitrary angle injection is designed to observe rotor position. The proposed high-frequency signal injection method minimises the zero-crossings of the phase current at any value of the torque angle. Both of the novel sinusoidal pulsating injection sensorless control scheme and square-wave injection sensorless control scheme are confirmed by experiments on a 2.2-kW interior permanent magnet synchronous motor (IPMSM) drive platform.

Alternate computation of the unit vectors synthesis towards synchronization of current-controlled grid-tie converter for renewable power system: An embedded outlook

Phase synchronization and frequency tracking are essential part of control unit design for the grid -tie power converter of the efficient energy conversion system. A robust but straightforward algorithm has been proposed here using a digital zero-crossing detector (ZCD) circuit. The ZCD is made to be vigorous by a D-latched based implementation against the multiple zero-crossings in the synchronizing signal at the point of the common coupling (PCC). The corresponding unit vectors comprising of the sine and cosine components is synthesized using trigonometric orthogonal properties (TOP) and implemented using field programable gate array (FPGA) by backward Eular’s method. The proposed approach is simulated using Altera Quartus II IDE on a target device CycloneEP1C12Q240C8. The performance of the unit vectors has been tested on current-controlled pulse width modulated (PWM) power converter for seamless energy conversion. The paper includes the contextual review, description of the scheme, analysis, implementation and experimental validation. The analytical findings and experimental results are well agreeing

Power quality enhancement in solar power with grid connected system using UPQC

The need to generate pollution free energy has triggered the effect towards the usage of solar energy interconnection with the grid. Consequently, the Photovoltaic (PV) panel interfaced with the grid causes the power quality problems such as a voltage harmonics and voltage distortion etc., Active power filters are the powerful tool for mitigation of harmonics. This work involves the use of single-phase Unified Power Quality Conditioner (UPQC) based on a unit vector template control algorithm for its functions with grid integration of photovoltaic, such as voltage sags/ swell, unit power factor correction, voltage and current harmonic cancelation. The unit vector template control algorithm includes a phase-locked loop (PLL) mechanism that is responsible for avoiding multiple zero crossings during highly distorted grid voltage detection. A unit vector template control with a PLL-based control algorithm is applied to the shunt and series inverters of PV grid connected UPQC. In addition to normalizing voltage and current disturbances, the proposed controller has the functions of phase detection and perfect grid synchronization. It is proposed that the system performance is fully verified by MATLAB simulation with the response of load variation, transient response, THD, voltage swell and sag. The Total Harmonic Distortions (THDs) of proposed grid integration of photovoltaic systems through single-phase unified power quality conditioner (UPQC) obtain the range of IEEE standard.

Alteration of Particle Drift Resonance Dynamics Near Poloidal Mode Field Line Resonance Structures

AbstractWe examine the effect on drift‐resonant particle dynamics of a strongly peaked internally driven poloidal mode field line resonance (FLR; with specified frequency ω in the Pc5 range and azimuthal mode number m≫1). Using an analytic magneto‐hydrodynamic model in a dipole field to describe the ultra low frequency wave mode, we use the bounce‐averaged formalism of Northrop (1963) to obtain equations of motion for charged particles in the wave frame and find an analytic solution for the case of a temporally constant ultra low frequency wave amplitude profile. Focusing on equatorially mirroring electrons in this study, we demonstrate that, for sufficiently peaked radial profiles, multiple drift resonances appear that are associated with the FLR peak. These are in addition to the well‐known zeroth‐order drift resonance location, occurring when the unperturbed drift speed satisfies the resonance condition ( ). The additional resonances arise because the strongly peaked FLR wave field components provide sufficiently strong perturbations to the azimuthal drift speed to cause multiple zero crossings in the resonance condition. These additional resonances have trapping periods much lower than that of the zeroth‐order resonance and considerably complicate the electron dynamics. Further properties of these resonances and their measurable effect on electron dynamics are discussed. For example, their effect on observations of energetic electron flux on board satellites in the vicinity of an FLR is calculated and shown to significantly distort the typical signature associated with drift resonance (modulations in electron flux at the wave frequency with a 180° phase change across the resonant energy).

Multi‐Timescale Analysis of the Spatial Representativeness of In Situ Soil Moisture Data within Satellite Footprints

We conduct a novel comprehensive investigation that seeks to prove the connection between spatial and time scales in surface soil moisture (SM) within the satellite footprint (~50 km). Modeled and measured point series at Yanco and Little Washita in situ networks are first decomposed into anomalies at time scales ranging from 0.5 to 128 days, using wavelet transforms. Then, their degree of spatial representativeness is evaluated on a per time-scale basis by comparison to large-spatial scale datasets (the in situ spatial average, SMOS, AMSR2 and ECMWF). Four methods are used for this: temporal stability analysis (TStab), triple collocation (TC), the percentage of correlated areas (CArea) and a new proposed approach that uses wavelet-based correlations (WCor). We found that the mean of the spatial representativeness values tends to increase with the time scale but so does their dispersion. Locations exhibit poor spatial representativeness at scales below 4 days, while either very good or poor representativeness at seasonal scales. Regarding the methods, TStab cannot be applied to the anomaly series due to their multiple zero-crossings and TC is suitable for week and month scales but not for other scales where datasets cross-correlations are found low. In contrast, WCor and CArea give consistent results at all time-scales. WCor is less sensitive to the spatial sampling density, so it is a robust method that can be applied to sparse networks (1 station per footprint). These results are promising to improve the validation and downscaling of satellite SM series and the optimization of SM networks.

A Three-Phase PLL Algorithm Based on Signal Reforming Under Distorted Grid Conditions

This paper proposes a novel three-phase phase-locked loop (PLL) algorithm, which focuses on the reforming of the primary signals before grid synchronization rather than improving the phase estimation methodologies. The unbalanced signals are reformed to balanced ones without damage to the phase angle, through which the negative sequence of the grid voltages is removed. This eliminates the estimation errors of conventional synchronous reference frame PLL and enhances its response speed with a higher bandwidth. The reforming process is supposed to be carried out at every zero-crossing point of the three-phase voltages and choose one phase as reference to balance the other two. Coefficients for the signal reforming are calculated at one zero-crossing point and updated until the next comes. In implementation, a certain phase is chosen as the reference all along and the reforming process will be suspended when it just crosses the zero line. This PLL algorithm has a fast and precise character to reform the three-phase grid voltages and is flexible for application. Under heavily distorted grid conditions, it can still perform effectively even with multiple zero-crossings. Comprehensive experimental results from a digital signal processor-based laboratory prototype are provided to validate the performance of this PLL algorithm.

Assessment of plasma impedance probe for measuring electron density and collision frequency in a plasma with spatial and temporal gradients

Numerical simulations and experimental measurements were combined to determine the ability of a plasma impedance probe (PIP) to measure plasma density and electron collision frequency in a plasma containing spatial gradients as well as time-varying oscillations in the plasma density. A PIP is sensitive to collision frequency through the width of the parallel resonance in the Re[Z]-vs.-frequency characteristic, while also being sensitive to electron density through the zero-crossing of the Im[Z]-vs.-frequency characteristic at parallel resonance. Simulations of the probe characteristic in a linear plasma gradient indicated that the broadening of Re[Z] due to the spatial gradient obscured the broadening due to electron collision frequency, preventing a quantitative measurement of the absolute collision frequency for gradients considered in this study. Simulation results also showed that the PIP is sensitive to relative changes in electron collision frequency in a spatial density gradient, but a second broadening effect due to time-varying oscillations made collision frequency measurements impossible. The time-varying oscillations had the effect of causing multiple zero-crossings in Im[Z] at parallel resonance. Results of experiments and simulations indicated that the lowest-frequency zero-crossing represented the lowest plasma density in the oscillations and the highest-frequency zero-crossing represented the highest plasma density in the oscillations, thus the PIP probe was found to be an effective tool to measure both the average plasma density as well as the maximum and minimum densities due to temporal oscillations.

Simple Model Based Dead Time Compensation Using Fast Current Measurement

Nowadays the increasing utilization of alternative energy sources demand three phase power converters capable of delivering high quality energy to the low voltage grid. Good dead time compensation hardware and software are essential to keep low order harmonics at acceptable levels even at light load conditions, at acceptable costs. Low current waveforms with multiple zero crossings within a switching period are still problematic with today's technology. Such operating conditions often happen in PWM inverters and in variable frequency drives at or below 10% load. This paper describes a new method which uses a model for calculating the voltage error caused by dead time for each phase leg. The method is completely software based, but requires fast current measurement. A model splits each half period of the triangular carrier to time segments where the slopes of the currents in all phases, and the output voltage of all semiconductor phase legs are constant. It determines the duration of each of the time segments, and integrates the volt-seconds for a half period of the triangular carrier. The model is capable of handling discontinuous conduction as well. The resulting error voltage can be used to calculate a new, compensated duty factor which can be applied to the PWM modulator. The described algorithm was tested via computer simulation. A comparison was made with other, previous methods using the same inverter model.

Modified sliding mode observer for wide speed range operation of brushless DC motor

This paper describes an adaptive gain sliding mode observer for brushless DC motor for large variations in speed. Sensorless brushless DC motor based on sliding mode observer exhibits multiple zero crossing in back electromotive force (EMF) which leads to commutation problems at low speed. In this paper, a modified sliding mode observer incorporating a speed component in the estimation of back EMF is proposed. It is found that after incorporating the speed component in the back EMF observer gain, multiple zero crossings at low speeds and phase shift at higher speeds are eliminated. The trapezoidal back EMF observer is implemented experimentally on a digital signal processor (DSP) board. The effectiveness of the proposed method is demonstrated through simulations and experiments.

An adaptive harmonic detection and a novel current control strategy for unified power quality conditioner

This paper proposes an adaptive harmonic detection to precisely detect the voltage with multiple zero crossings and adaptively obtain the reference signals, which makes use of linear neurons to approximate the fundamental component in each phase followed by a symmetric decomposition that calculates the fundamental positive components. According to the compensating requirements, we obtain four different forms of the reference signals. The detected reference signals are then fed into a triangular wave comparison control together with a PI controller and a one cycle current control to force the compensating voltage and current to track the reference signals. The one cycle current control (OCCC) is a combination of the one cycle control and the hysteresis control, which guarantees both tracking performances and constant frequency. The integration of the adaptive detection method and the one cycle current control in a three-phase unified power quality conditioner (UPQC) are simulated, where the effectiveness and reliability of the proposed strategies are demonstrated.

Pulsating Signal Injection-Based Axis Switching Sensorless Control of Surface-Mounted Permanent-Magnet Motors for Minimal Zero-Current Clamping Effects

In this paper, we propose an injection-based axis switching (IAS) sensorless control scheme using a pulsating high-frequency (HF) signal to minimize position detection error and velocity estimation ripple resulting from the zero-current-clamping (ZCC) effect for surface-mounted permanent-magnet motors. When a pulsating carrier-signal voltage is injected in an estimated synchronous frame, the envelope of the resulting HF current measured in the stationary reference frame follows an amplitude-modulated pattern. Using this information, the IAS technique allows one to avoid multiple zero crossings of HF currents by adjusting the current phase angle according to the load condition. At no-load condition, the pulsating voltage is injected only on the d-axis, while the d-axis current is controlled to a certain nonzero value. Under a load condition, the injection voltage is switched to the q-axis, while the d -axis current drops back to zero. Thus, the proposed sensorless control enforces a much better estimation performance in a region of ZCC without a predefined offline commissioning test than the standard pulsating injection scheme. Experiments illustrate the effectiveness of the proposed method in suppressing the estimation error caused by the ZCC disturbance and in extending the system bandwidth.

Voltage Multiple-Zero-Crossings at Buses Feeding Large Triac-Controlled Loads

Triac-controlled loads operating in three-phase four-wire electric networks produce large zero-sequence current harmonics that cause large currents in the neutral conductor. Under certain conditions, the phase-to-neutral voltage (PTNV) at the bus feeding a large triac-controlled load is distorted to such a degree that multiple zero crossings (MZC) appear in the voltage waveform. This situation may cause malfunction of the triac control systems or any other control systems that are based on the detection of voltage zero crossings. The influence of various parameters of the triac-controlled load and of the cable feeding it, on the appearance of voltage MZC, is investigated. A simulation model is built with alternative transients program version of Electromagnetic Transients Program and is validated by comparison with measurements taken at a real theatrical lighting installation controlled by triacs. The occurrence of MZC in the voltage waveform is also explained by an analytical approximation. It is shown that certain cable configurations should be avoided when feeding large triac-controlled loads, or otherwise, MZC will appear in the PTNV.

Wavelet coefficients for window width and subsequent harmonics estimation – Case study

This paper is an extended version of the original author’s work presented during XIV IMEKO TC-4 Symposium [T. Tarasiuk, Estimation of measurement window width by interpolation based on wavelet coefficients – case study, in: Proceedings of 14th IMEKO TC-4 International Symposium, Poland, Gdynia/Jurata 2005, pp. 352–357]. Especially, new results have been added. This paper deals with the problem of reliable width estimation of a measurement window and its impact on harmonic analysis of chosen signals. The simple method of window width estimation is detection of a zero-crossing instant of a given signal by the analysis of sample polarisation changes. But the method is sensitive to waveform distortions, especially analysed signal multiple zero-crossings. So, the idea of implementing a discrete wavelet transform for risk reduction of measurement results corruption by the higher frequency phenomena has been proposed and preliminarily tested [T. Tarasiuk, Interpolation based on wavelet coefficients for frequency measurement, in: Proceedings of XVII IMEKO World Congress, June 22–27, 2003, Dubrovnik, Croatia, pp. 895–898]. In this paper, the concept has been further developed, especially the analysis of real voltages with multiple zero-crossing has been carried out. Then, the consequences of the chosen methods for the subsequent harmonics analysis have been laid and discussed.

Nature of insulator–metal transition and novel mechanism of charge transport in the metallic state of highly doped electronic polymers

Highly conducting polymers such as polyaniline and polypyrrole in a metallic state have unusual frequency dependent conductivity, including multiple zero crossings of the dielectric function. A low frequency electromagnetic response, when be analyzed by the Drude theory of metals, is provided by an extremely small fraction of the total number electrons ∼0.1%, but with extremely high mobility or anomalously long scattering time ∼10 −12 s. We show that a network of metallic grains connected by resonance quantum tunneling has a Drude type response for both the high and low frequency regimes and behaves as a dielectric at intermediate frequency in agreement with experimental observations. The metallic grains in polymers represent crystalline domains of well-packed chains with delocalized electrons embedded in the amorphous media of poor chain order. Intergrain resonance tunneling occurs through the strongly localized states in amorphous media. The small concentration of electrons participating in dc-transport is assigned to the low density of resonance states, and the long relaxation time is related to the narrow width of energy levels in resonance.

A general formula for prediction of iron losses under nonsinusoidal voltage waveform

A simple and efficient method for the estimation of iron loss under any nonsinusoidal voltage without multiple zero crossings (i.e. without minor hysteresis loops) is proposed. This method is based on the loss separation model, where iron loss is decomposed into hysteresis, classical and excess loss components. The voltage waveform is identified by the form factor coefficient, easily accessible. Knowledge of the voltage harmonic spectrum is not required in this method. The cases of rectangular pulse, PWM, and fundamental plus a controlled third harmonic voltage are treated and a satisfactory prediction of iron loss is obtained.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>